Radio transmission in a mobile network may be subject to various types of impairment. For example, downlink (DL) radio transmissions to a user equipment (UE) in a cell of the mobile network may be subject to interference from DL radio transmissions in another cell. By way of example, such problems may arise when utilizing a heterogeneous deployment with high power base stations, also referred to as macro base stations, and low power base stations, also referred to as pico base stations. In such heterogeneous deployment, a conventional cell association mechanism which is based on DL received signal strength typically results in a limited coverage area of the pico base stations. The coverage area may however be extended by adding a bias to the DL received signal strength of a pico base station as measured by the UEs, and using the biased DL received signal strength in the cell association mechanism. This has the effect that also UEs near the cell border, which measure a lower DL received signal strength, will be associated with the cell so that the cell coverage area is extended. However, this may also have the effect that certain UEs experience a negative (on the logarithmic scale) Signal-to-Interference/Noise Ratio (SINR). In particular, the added bias may have the effect that a UE is associated with the pico base station, but the DL received signal strength from a macro base station is larger than the measured (unbiased) DL received signal strength of the pico base station. The interference from the macro base station is thus larger than the useful radio signal from the pico base station. The interference may affect both a data channel of the cell and a control channel of the pico base station's cell.
The negative SINR may thus cause failure of radio transmissions on the control channel. Such failures may adversely affect the overall performance of the cell. For example, the control channel may be used to indicate scheduling decisions of the network to the UEs in the cell. A radio transmission on the control channel may then for example indicate radio resources of the data channel in which a DL radio transmission to the UE is scheduled. However, a failure of the radio transmission on the control channel, which indicates the radio resources, will then have the effect that the DL radio transmission on the data channel cannot be received by the UE and will fail as well. The scheduled resources are therefore wasted.
To address the above interference problems, techniques for interference protection may be used. For example in mobile networks using LTE (Long Term Evolution) radio access technology specified by 3GPP (3rd Generation Partnership Project), certain resources may be protected from interference by defining an Almost Blank Subframes (ABSs). In an ABS, the macro base station does not transmit any data, but typically only Cell Specific Reference Symbols (CRSs) and possibly some control information. The ABS may then be used for low-interference radio transmissions to the UEs in the cell of the pico base station. As an alternative to ABSs, also Reduced Power Subframes (RPSs) may be used, in which the macro base stations transmit at a reduced power level, thereby reducing the interference to the cell of the pico base station.
The utilization of ABSs and/or RPSs needs to be taken into account in the scheduling mechanism implemented at the pico base station. For example, the scheduling mechanism may first determine a set of UEs suffering from a negative SINR due to the interference from the macro base station(s), using the DL received signal strength reported by the UEs in the cell, and use exclusively resources from the ABSs for scheduling radio transmission of these UEs. This may degrade the performance experienced by these UEs, e.g., because the ABSs offer only limited resources, which may be insufficient to meet the demand of certain UEs. That is to say, while negative effects due to interference may be avoided by using ABSs or RPSs, this may come at the cost of degraded performance due to limited resources. Known scheduling algorithms, for example based on a channel quality of the data channel as described in “Frequency Domain Scheduling for E-UTRA”, submitted as document R1-060877 for 3GPP RAN1 meeting #44 bis (Athens, Greece, Mar. 27-31, 2006), are not suitable to address such issues.
Accordingly, there is a need for techniques which allow for efficiently controlling radio transmissions in a mobile network.